Nintendo has been seeing a sort of creative renaissance as of late, particularly regarding New IP. 2015 introduced Splatoon, the company's most successful original game in almost a decade. And just 2 years later, followed it up with ARMS, which while not as successful, still has a loyal following and is one of the best selling Fighting games this gen. If we continue to follow the bi-annual schedule, then Nintendo will introduce at least one new Mascot-driven IP in a similar vein to those 2 every other year, continuing in 2019. Shinya Takahashi has said that Nintendo has a lot of new and original ideas lined up for Switch, and that includes new mainstream character driven stuff like ARMS and Splatoon. A lot of projects Nintendo started around the time the Switch launched, will more than likely be ready beginning next year, so we should probably expect a new Splatoon/ARMS-like game that uses the Switch hardware in a unique way.
Personally, I would like to see something more single player driven this time.